WASHINGTON, Aug. 22 — The Bush administration is set to issue a regulation on Friday that would enshrine the coal mining practice of mountaintop removal. The technique involves blasting off the tops of mountains and dumping the rubble into valleys and streams.

It has been used in Appalachian coal country for 20 years under a cloud of legal and regulatory confusion.

The new rule would allow the practice to continue and expand, providing only that mine operators minimize the debris and cause the least environmental harm, although those terms are not clearly defined and to some extent merely restate existing law.

The Office of Surface Mining in the Interior Department drafted the rule, which will be subject to a 60-day comment period and could be revised, although officials indicated that it was not likely to be changed substantially.

The regulation is the culmination of six and a half years of work by the administration to make it easier for mining companies to dig more coal to meet growing energy demands and reduce dependence on foreign oil.

Government and industry officials say the rules are needed to clarify existing laws, which have been challenged in court and applied unevenly.

A spokesman for the National Mining Association, Luke Popovich, said that unless mine owners were allowed to dump mine waste in streams and valleys it would be impossible to operate in mountainous regions like West Virginia that hold some of the richest low-sulfur coal seams.

All mining generates huge volumes of waste, known as excess spoil or overburden, and it has to go somewhere. For years, it has been trucked away and dumped in remote hollows of Appalachia.

Environmental activists say the rule change will lead to accelerated pillage of vast tracts and the obliteration of hundreds of miles of streams in central Appalachia.

“This is a parting gift to the coal industry from this administration,” said Joe Lovett, executive director of the Appalachian Center for the Economy and the Environment in Lewisburg, W.Va. “What is at stake is the future of Appalachia. This is an attempt to make legal what has long been illegal.”

Mr. Lovett said his group and allied environmental and community organizations would consider suing to block the new rule.

Mountaintop mining is the most common strip mining in central Appalachia, and the most destructive. Ridge tops are flattened with bulldozers and dynamite, clearing all vegetation and, at times, forcing residents to move.

The coal seams are scraped with gigantic machines called draglines. The law requires mining companies to reclaim and replant the land, but the process always produces excess debris.

Roughly half the coal in West Virginia is from mountaintop mining, which is generally cheaper, safer and more efficient than extraction from underground mines like the Crandall Canyon Mine in Utah, which may have claimed the lives of nine miners and rescuers, and the Sago Mine in West Virginia, where 12 miners were killed last year.

The rule, which would apply to waste from both types of mines, is known as the stream buffer zone rule. First adopted in 1983, it forbids virtually all mining within 100 feet of a river or stream.

The Interior Department drafted the proposal to try to clear up a 10-year legal and regulatory dispute over how the 1983 rule should be applied. The change is to be published on Friday in The Federal Register, officials said.

The Army Corps of Engineers, state mining authorities and local courts have read the rule liberally, allowing extensive mountaintop mining and dumping of debris in coal-rich regions of West Virginia, Kentucky, Tennessee and Virginia.

From 1985 to 2001, 724 miles of streams were buried under mining waste, according to the environmental impact statement accompanying the new rule.

If current practices continue, another 724 river miles will be buried by 2018, the report says.

Environmental groups have gone to court many times, with limited success, to slow or stop the practice. They won an important ruling in federal court in 1999, but it was overturned in 2001 on procedural and jurisdictional grounds.

The Clinton administration began moving in 1998 to tighten enforcement of the stream rule, but the clock ran out before it could enact new regulations. The Bush administration has been much friendlier to mining interests, which have been reliable contributors to the Republican Party, and has worked on the new rule change since 2001.

The early stages of the revision process were supported by J. Stephen Griles, a former industry lobbyist who was the deputy interior secretary from 2001 to 2004. Mr. Griles had been deputy director of the Office of Surface Mining in the Reagan administration and is knowledgeable about the issues and generally supports the industry.

In June, Mr. Griles was sentenced to 10 months in prison and three years’ probation for lying to a Senate committee about his ties to Jack Abramoff, the lobbyist at the heart of a corruption scandal who is now in prison.

Interior Department officials said they could not comment on the rule because it had not been published. But a senior official of the Office of Surface Mining said the stream buffer rule was never intended to prohibit all mining in and around streams, but rather just to minimize the effects of such work.

Even with the best techniques and most careful reclamation, surface or underground mining will always generate mountains of dirt and rock, he said.

“There’s really no place to put the material except in the upper reaches of hollows,” the official said. “If you can’t put anything in a stream, there’s really no way to even underground mine.”

He said the regulation would explicitly state that the buffer zone rule does not apply for hundreds of miles of streams and valleys and that he hoped, but did not expect, that the rule would end the fight over mine waste.

Mr. Lovett of the Appalachian Center said the rule would only stoke a new battle.

“They are not strengthening the buffer zone rule,” he said. “They are just destroying it. By sleight of hand, they are removing one of the few protections streams now have from the most egregious mining activities.”